Calling base methods from member initializer list

Question

Is it safe to call non-virtual base methods from member initializer list? And virtual?

Answer 1

It is not safe to call any member function (virtual or not virtual) before all base have been initialized. Bellow an example given in the standard ([class.base.init]§16):

class A {
public:
  A(int);
};

class B : public A {
  int j;
public:
  int f();
  B() : A(f()),     // undefined behavior: calls member function but base A not yet initialized
  j(f()) { }        // well-defined: bases are all initialized
};

class C {
public:
  C(int);
};

class D : public B, C {
  int i;
public:
  D() : C(f()),     // undefined behavior: calls member function but base C not yet initialized
  i(f()) { }        // well-defined: bases are all initialized
};

There are more subtle cases.